Ultraviolet (UV) light or radiation is classified as UVA, UVB and UVC depending upon the wavelength thereof, UVA being the longest of the three at 320-400 nm. UVA is further divided into two wavelength ranges, UVA I measuring 340-400 nm and UVA II measuring 320-340 nm. UVB wavelength ranges from 290 to 320 nm. Both the UVA and UVB radiations penetrate into the atmosphere and play an important role in causing health problems and conditions such as premature skin aging, eye damage (including cataracts) and skin cancers. Shorter rays of UVC in the wavelength range of 100 to 290 nm are mostly absorbed by the ozone layer and do not reach the earth. Harmful effects of UV-B radiation may be aggravated by UV-A radiation. In order to prevent and mitigate the harmful effects of exposure to UVA and UVB radiations, there are several sunscreen, cosmetic or dermatological formulations available for topical application to human skin or hair, which comprise one or more UV absorbers or UV filters.
UV filters used in the sunscreen preparations are mainly derivatives of 3-benzylidenecamphor, ethylhexyl salicylate, p-methoxy-cinnamic acid esters such as 2-ethylhexyl p-methoxycinnamate or octyl-methodycinnamate (2-ethylhexyl(2E)-3-(4-methoxyphenyl)pro-2-enoate) or dibenzoylmethane derivative such as 1-(4-methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione or 4-(tert-butyl)-4′-methoxydibenzoyl methane (also called avobenzone, CAS No 70356-09-1). Some of the UV absorbing organic compounds employed in sunscreen compositions, avobenzone in particular, undergo rapid photo degradation on exposure to UV radiation and do not give effective protection from sun damage over a period of time. To overcome this problem, sunscreen preparations generally contain photostabilizers to enhance their photostability.
Deflandre et al teach stabilization of dibenzoylmethane derivative in a cosmetic composition comprising a cosmetically acceptable vehicle containing at least one fatty phase and alkyl β-β-diphenylacrylate or α-cyano-β-β-diphenylacrylate (U.S. Pat. No. 5,576,354). Raspanti et al teach photostable cosmetic compositions comprising combination of dibenzoylmethane derivative and benzopheride derivative (U.S. Pat. No. 5,776,439). Bonda et al describe a sunscreen composition comprising dibenzoylmethane derivative such as 4-(1,1-dimethylethyl)-4′-methoxydibenzoylmethane and a benzoate stabilizer for the dibenzoylmethane derivative (U.S. Pat. No. 5,788,954). Bonda et al also describes a sunscreen composition comprising dibenzoylmethane derivative stabilized with salicylate (U.S. Pat. No. 5,849,273).
Gonzenbach et al teach cosmetic compositions comprising at least one fatty phase, dibenzoymethane derivative and water soluble p-methoxycinnamate derivative stabilized with 3,3-diphenylacrylate derivative or benzylidene camphor derivative (U.S. Pat. No. 5,985,251). The term “water-soluble p-methoxycinnamate derivative” refers to compounds such as ammonium-, sodium-, potassium-p-methoxycinnamate, salts of primary, secondary or tertiary amines of p-methoxycinnamic acid like mono-, di- or triethanol amine salts, aminomethyl-propanol salt, morpholine salt and the like. Preferred are mono-, di-, and triethanolamine salts. p-Methoxycinnamate derivative and 3,3-diphenylacrylate derivative are used as stabilizers for avobenzone.
Gonzenbach also teach photostable, cosmetic sunscreen composition comprising dibenzoylmethane derivative stabilized with α-cyano-β,β diphenylacrylate (U.S. Pat. No. 6,033,649). Cole et al teach sunscreen compositions comprising a dibenzoylmethane derivative stabilized with a combination of a benzophenone derivative and a diester or polyester of a naphthalene dicarboxylic acid (U.S. Pat. No. 6,444,195). Meyer et al describe sunscreen compositions containing avobenzone and zinc oxide stabilized with phenylbenzimidazole sulfonic acid (U.S. Pat. No. 7,244,416). Wagner et al teach a sunscreen composition comprising dibenzoylmethane derivative stabilized with merocyanine derivatives (U.S. Pat. No. 8,535,648).
Nambudiry et al teach a sunscreen composition suitable for topical application to human skin or hair to provide protection from excessive exposure to ultra-violet rays, which comprises an effective amount of a substituted 1,3-diketone which is 1,3-propanedione,1-(4-methoxy-5-benzofuranyl)-3-phenyl(pongamol) and physiologically acceptable vehicle for the substituted 1,3-diketone. The 1,3-diketone forms from 0.01 to 15% by weight of the composition. (U.S. Pat. No. 5,152,983).
In the above compositions, photostabilizers, wherever used, are all synthetic compounds which are generally considered to be unsafe for the users. Preparation of synthetic compounds generally gives rise to byproducts which create environmental hazards and problems. Octyl-methoxy cinnamate is oil soluble and water insoluble. Water-soluble p-methoxy cinnamate derivative and octyl-methoxy cinnamate are distinctly different compounds and are not chemical equivalents or substitutes for each other. Avobenzone is also oil soluble and water insoluble.
There is thus need for sunscreen compositions comprising and stabilized with natural photostabilizers, which are safe, environment friendly and cost effective.